An example of typical adjustable wrench 10 found in the prior art is shown in FIGS. 1A and 1B. Wrench 10 is comprised of three main pieces, namely body 11 (which includes handle 12 and upper jaw 14), lower jaw 16, and thumbwheel 17. As one skilled in the art will immediately recognize, lower jaw 16 contains angled threads 18 which intermesh with similarly angled threads 20 on thumbwheel 17 in a screw-like fashion such that when thumbwheel 17 is rotated, lower jaw 16 will move to or from upper jaw 14 depending on the direction of rotation.
During manufacture, main body 11 is typically formed of hot forged steel. Then a bore hole 30 and slot 32 are formed in main body 11 to allow lower jaw 16 to be slid within. Bore hole 30 is formed by drilling a hole in the main body 11, usually straight through to the top of the handle. Then, slot 32 can be formed by a saw, usually a reciprocating broach bar. After bore hole 30 and slot 32 are formed, lower jaw 16 can be slid into place within main body 11. Thereafter, thumbwheel 17 is slipped into place so as to mesh threads 18 and 20 and is then permanently attached to main body 11 by a rivet 34.
The steps of forming bore hole 30 and slot 32 in the main body 11 add significant expense to the cost of manufacturing wrench 10. Moreover, the design of wrench 10 tends to rattle in the hand of the user when shaken. This is due to the fact that the lower jaw 16 is held steady within the bore hole 30 and slot 32 by its mechanical connection with thumbwheel 17. As shown in the cross-sectional view of FIG. 2, and due to the generally cylindrical shape of thumbwheel 17, thumbwheel 17 (or more specifically the threads 20 of the thumbwheel 17) comes into contact with the lower jaw 16 (or more specifically the threads 18 of lower jaw 16) at a single point. Because lower jaw 16 and thumbwheel 17 are not securely braced against one another, the lower jaw 16 will rattle in the user's hand when shaken back and forth in direction 25. This unsteadiness is perceived by prospective purchasers as being indicative of a wrench that is not constructed with good mechanical tolerances and hence is of poor quality.
The present invention solves these problems of the prior art by providing an improved design for an adjustable wrench which is less costly to manufacture and more stable in the user's hands.